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M. Brandstetter, A. Genner, G. Ramer, J. Kasberger, B. Lendl:
"Quantum cascade laser based optical sensors for chemical analyses in the liquid phase";
Vortrag: 8. ASAC JunganalytikerInnen Forum, Paris-Lodron-Universität Salzburg; 01.06.2012 - 02.06.2012; in: "8. ASAC JunganalytikerInnen Forum - Program & Book of Abstracts", (2012), S. 21.

The implementation of mid-IR Quantum Cascade Lasers (QCL) in liquid phase absorption spectroscopy opens a broad field of potential applications, e.g. in clinical analysis and process analytical chemistry [1]. There, the key features of QCLs, such as high spectral power density and compact design make them suitable for portable sensor applications.
In liquid phase spectroscopy with QCLs tunability and high emission power are crucial, especially when measuring in highly absorbing matrices, e.g. in water. Both requirements were met by the employed broadly tunable External Cavity QCL (EC-QCL). An essential step towards high reproducibility in the measurements using this new mid-IR laser source was a thorough investigation of its time-resolved spectral characteristics. This was achieved using step-scan FTIR measurements in order to characterize pulse-to-pulse power fluctuations and spectral non-linearities.
An alternative approach to EC-QCLs can be the use of arrays of single-mode QCLs. In this context novel surface-emitting ring-cavity QCLs [2] are promising tools. Due to their ring-cavity design they offer enhanced emission characteristics compared to standard Distributed Feedback (DFB) QCLs. Moreover they enable compact sensor designs as they emit at very low divergences, which could make the use of lenses obsolete.
Furthermore, emerging technologies such as single-mode slab-waveguides (which offer a higher interaction pathlength with the evanescent field) for surface sensitive sensor concepts will be discussed. The combination of QCLs with these single-mode waveguides can facilitate compact sensor setups with the advantage of an enhanced sensitivity compared to conventional ATR measurements.
REFERENCES
1 Brandstetter, M., "Tunable external cavity quantum cascade laser for the simultaneous determination of glucose and lactate in aqueous phase", Analyst 135, 3260-3265 (2010)
2 Mujagic, E., "Ring-cavity surface emitting lasers as a building block for tunable and coherent quantum cascade laser arrays ", Semicond. Sci. Technol., 26, 1-6 (2011)
Acknowledgements:
Financial support was provided by the Austrian research funding association (FFG) under the scope of the COMET programme within the research network "Process Analytical Chemistry (PAC)"

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